Conventional cable systems can utilize a cable modem to transmit and to receive data across a coaxial cable or line. The cable couples a head end or central office to numerous pieces of video equipment disposed in a multitude of residences.
Cable systems are generally utilized as one-way systems in which cable television signals are transmitted from the head end to the video equipment coupled to the cable. The video equipment can include video cassette recorders (VCRs), television units, or other devices. The cable television signals are transmitted in a frequency range from approximately 50 megahertz (MHz) to 550 MHz. The video equipment receives the cable television signals and either provides images in accordance with the cable television signals or stores the cable television signals.
Cable modems can be utilized with existing cable systems to communicate data bidirectionally between the home and the head end. The cable modem transmits data from the home to the head end in a frequency range between approximately 5-39/42 (e.g., on a return channel). Generally, the return channel can utilize a 5-39 MHz range (low split) or a 5-42 MHz range (mid split). The cable modem receives data from the head end in a frequency range between 550-750 MHz (e.g., the downstream channel). The high-speed, downstream channel is often utilized to provide digitized services, such as, digitized entertainment to the residence, or to provide other data communications to the residence.
The return channel is typically utilized to transmit small amounts of data, such as, requests for download information, while the downstream channel is utilized to transmit large amounts of data, such as, data associated with video signals, large programs, documents, or other applications. For example, in most internet applications, larger amounts of data are requested by the residential user than by the internet source. Further, in pay-per-view movie applications, the return channel is utilized to transmit relatively small data files, including billing and addressing information, while the downstream channel is utilized to transmit the relatively large data file, including the movie.
The conventional return channel is not adequate for all cable modem applications, especially applications in which larger amounts of data must be transmitted to the head end. Heretofore, the return channel associated with conventional cable modems can be susceptible to interference from a number of other radio frequency (RF) sources, including amateur radio units and household motors, which provide distortion in the 5-39/42 MHz range. Additionally, the bandwidth associated with the conventional return channel (e.g., 5-39/42 MHz) is somewhat limited, thereby restricting the amount of data which can be sent to the head end.
Since the frequency range between 50-550 MHz is utilized by all television sets coupled to the cable, it cannot conventionally be used for return channel applications. Indeed, the reception of all television sets would be affected by any signal placed in the frequency band between 50-550 MHz. Accordingly, conventional cable modems must transmit and receive data outside of the 50-550 MHz range to protect the reception of the large number of customers who are already committed to this aspect of the cable system. Thus, data cannot normally be transmitted upstream in the 50-550 MHz frequency range because of the multi-drop nature of the cable system.
Thus, there is a need for a high-speed return channel for cable modems. Further still, there is a need for more efficient use of the frequency band between 50-550 MHz in a cable system.